Abstract: The perturbation formulas of the electron paramagnetic resonance (EPR) parameters g factors g//, g⊥ and the hyperfine structure constants A//, A⊥ are established for a 3d1 ion in tetragonally distorted octahedra, by including the contributions from the p-and s-orbitals as well as the spin-orbit coupling of the ligands based on the cluster approach. The related energy separations can be obtained from the superposition model (SPM) and local structure of impurity center. These formulas are applied to the studies of the EPR parameters for the interstitial V4+ in anatase (TiO2). The calculated results of present work show better agreement than those of the previous studies with the observed values. It can be found that the contributions to the EPR parameters from the ligand orbitals and spin-orbit coupling interactions cannot be neglected for the systems with significant covalency.